Projection camera: This parameter specifies the camera used for Through camera image projection. If no camera is specified the camera rendering the scene is used.

Unpremultiply colour,Unpremultiply translucency,Unpremultiply luminosity,Unpremultiply reflectivity,Unpremultiply specular roughness:
All of the above checkboxes apply to the corresponding image parameter. For example the Unpremultiply colour checkbox applies to the diffuse Colour imageparameter. If a checkbox is checked then the appropriate image is unpremultiplied. Some images use premultiplied alpha and may give incorrect results if they're not unpremultiplied. If you know an image doesn't have an alpha channel you don't need to make any changes.

A shader is a program or set of instructions used in 3D computer graphics to determine the final surface properties of an object or image. This can include arbitrarily complex descriptions of light absorption and diffusion, texture mapping, reflection and refraction, shadowing, surface displacement and post-processing effects. In Terragen 2 shaders are used to construct and modify almost every element of a scene.

A parameter is an individual setting in a node parameter view which controls some aspect of the node.